Large power supply systems offer protection arrangements to shutdown the system if regulated voltage and current conditions exceed predefined alarm limits. Frequently both high and low alarm limits are centered around a voltage or current regulation characteristic. Since regulation characteristics have a slope in the VI plane, alarm limits centered about one operating point are not still centered if the operating point of the power supply drifts or is changed to some other portion of the regulation characteristic curve. This places a restriction upon the tightness of the alarm tolerances permitted.